One form of particulate inorganic porous material useful in the invention is controlled pore glass (CPG) described in U.S. Pat. Nos. 3,549,524 and 3,758,284 commercially available from CPG, Inc., 3 Borinski Road, Lincoln Park, N.J. 07035. It is widely used in methods for the synthesis of nucleic acids and for the isolation or purification of nucleic acids and proteins.
U.S. Pat. No. 3,890,417 describes a method for making a porous diaphragm suitable for use in electrolytic cells. The diaphragm is formed as a sheet from aqueous polytetrafluoroethylene (PTFE) and a solid, non-porous particle additive. Porosity is imparted to the product by removal of the particulate additive. U.S. Pat. No. 4,153,661 describes a similar method for making high tensile strength PTFE composite sheet material from aqueous PTFE, and organic or inorganic particles which comprises mixing and calendering at an elevated temperature (50-100.degree. C.) to produce a self-supporting film for use as an electronic insulator.
U.S. Pat. Nos. 4,373,519, 4,460,642, 4,565,663 and 4,971,736 disclose methods for making water-swellable composite sheets having hydrophilic, absorptive particles enmeshed in the PTFE matrix for use as wound dressing and chromatographic supports.